The present invention relates to an improvement in the method for the preparation of a semiconductor silicon single crystal or, in particular, N-type semiconductor silicon single crystal by the Czochralski method and a fused silica glass crucible used therefor.
As is well known, semiconductor silicon single crystals are mostly prepared by the so-called Czochralski method or pulling-up method in which a silicon single crystal as growing on the lower end of a seed crystal is pulled up from a melt of high-purity silicon formed by melting polycrystalline silicon in a crucible of fused silica glass. One of the problems in the silicon single crystal prepared by this crystal growing method is that so-called "oxidation-induced stacking fault", referred to as OSF hereinafter, are sometimes found therein. These OSFs are very detrimental in the subsequent manufacturing process of integrated circuit devices and the like from wafers of the silicon single crystal resulting in a great decrease in the yield of acceptable products of integrated circuits and the like so that it is eagerly desired to develop a method by which silicon single crystals absolutely free from occurrence of OSFs can be grown.
As an approach to accomplish a decrease in the density of OSFs to a significant extent, proposals have been made in recent years for the use of polycrystalline silicon having a still higher purity than heretofore as well as materials of the structure of the pulling-up furnace having an extremely high purity, improvements in the conditions for crystal growing and use of a fused silica glass crucible having the highest purity available.
In connection with the above described problem due to occurrence of OSFs, an interesting phenomenon has come to the attention of the artisan in an N-type silicon single crystal, which is a semiconductor silicon doped with a dopant of the Vth-Group elements in the Periodic Table such as phosphorus, antimony, arsenic and the like, that, when a silicon single crystal absolutely free from OSFs by the inspection immediately after completion of the crystal growing is kept standing as such, i.e. in the form of a single crystal rod, for a certain length of time or, for example, for one month or longer at room temperature, a large number of OSFs are sometimes detected by the subsequent inspection. This phenomenon is referred to as the delayed OSF hereinafter. Though not well understood, it is a presumable mechanism of this phenomenon of delayed OSF that the impurities contained in the starting single crystal rod in a very trace amount cause diffusion through the single crystal rod during storage at room temperature to form aggregates which serve as the nuclei for the occurrence of OSFs. As a consequence of the presumption of the mechanism, proposals have been made by the inventors in Japanese Patent Kokai 5-58800 to avoid the phenomenon of delayed OSF according to which the single crystal rods are stored at a temperature as low as possible to retard diffusion of impurities or the single crystal rods are sliced into wafers as early as possible so as to block the diffusion.
The above proposed methods, however, are nothing more than a method for the prevention or retardation of the delayed OSFs in a silicon single crystal having inherency toward occurrence of OSFs sooner or later providing no fundamental solution of the problem if not to mention the secondary problems unavoidable therein that the low-temperature storage of silicon single crystal rods is a very expensive way to significantly increase the production costs and the early slicing of the single crystal rods into wafers is accompanied by great difficulties in the production planning and storage of the wafers as sliced. Therefore, a complete solution of the OSF problem can be obtained only by the establishment of a method for the preparation of a silicon single crystal which is free not only from occurrence of OSFs immediately after single crystal growing but also from the delayed OSFs even after a prolonged storage of the single crystal rods as grown at room temperature.